Paper sizing



Patented June 1, 1943 APEE SIZING Paul iii Davidson, Wilklnsburg, Pa., assignor to Strathmore Paper Company, West Springfield, Mass, a corporation of Massachusetts No Drawing. Application December 19, 1939, .Serial No. 310,040

6 Claims. '(C'l. 106135) This, invention relates to the art of sizing paper with a' composition including animal glue.

It is common practice in the manufacture of certain types of paper to apply a surface treatment or sizing of animal glue to the paper for the purpose of imparting to the paper certain characteristics such as strength, greater resistance to the penetration of such liquids as inks, improved erasure propertiesfincreased durability and permanence and stiffness. In somespeciallty papers, such as blueprint vpaper, there-"are'the and resistance to abrasion when the papea wetted or soaked in water during the developixi of the exposed prints with the paperu'nder ten- I sion, and often with the water applied under pressure.

The ordinary production of the paper base includes an operation of engine sizing in which a sizing such as rosin emulsion is introduced into the beater with the paper stock, and an opera-- tion is performed for precipitating the rosin as its size, for example, by the introduction of paper maker's alum (aluminum sulfate). This paper stock is then formed into the paper, and is then given a glue sizingfor the purposes herein set forth; for example; such papers are passed through a-bath of animal glue and then between rolls that squeeze oil the excess of glue, after which the paper is treated in some manner with a tanning agent to set the glue to a water resistant material]. In the prior art, the glue solution is usually applied to the paper at 'a temperature of about 1.40 degrees P. so that, due to its lower viscosity at this temperature, it will paper gives rise to difliculties in the tub sizing operations. In some instances, for example, the

,first part of a web which is run through a glue size may have desirable properties, whereas a later part of the web may be objectionably bad: and there is not the uniformity of treatment and condition from one end of such a web to the other, so that later coatings may .be applied with expectancy of a uniform result. This effect is especially pronounced with 100 percent rag papers. This change of condition apparently in added requirements of suflicienttensile strength part arises from a leaching of the alum from the paper into the tub size, with a reduction of the penetrate into the paper and produce a more or less complete saturation of the paper with the glue size.

- For some special types of paper, such as blueprint paper, this method of glue sizing doesnot produce the best results. ;With the development of more improved blueprint coating and printing machines, a paper so sized does not possess V adequate wetstrength properties; the sensitized paper does not print with sufliclent rapidity to solution on or near the surface of the'paper.

produce dark bright -blue colored prints; the

blueprint coating or sensitizing solutions do 'not evenly wet the paper which results in prints covered with small white spots; there is a decided lack of uniformity in the properties of the sized paper; and the sensitized paper is subject to more or less rapid spoiling which reduces the contrast between the white lines and the blue background of the prints. v

The presence of the aluminum sulfate in the the time it is applied to the paper which prevents pH value of this size to a point below substantially pH 8. It has been found that by employment of a buffering agent, this behavior of the .material is compensated throughout the normal course of commercial runs with the usua1 quan-- tities of sizing solution in the sizing tub.

The sizing treatment is advantageous forthe preparation of so-called blueprint papers, which are afterward given a coating of the sensitizing solution. It is also advantageous in the preparation of negative papers, which normally are made 'An improved color and speed of printing of the blueprints is provided by retaining the sensitizing With a given speedof the coating machine, a given amount of sensitizing solution is'apphed to the paper in a given length of time. If is concentrated on or near the surface of the paper and not-allowed to penetrate excessively into the P per, more of the blueprint chemicals are ex- .posed to the light in a given printing time.

the concentration of the color produced is in- Thus creased and the printing can be reduced. This feature of the invention is preferably accomplished (1*) by incorporating into the glue size an inert material that swells in and imbibes water; (2) by a lowered temperature of the glue size at excessive penetration of the glue. into the paper. This is based upon the discovery that the sensitizwhite spots when sensitized and printed, and the better keeping properties of the sensitized paper, are attained by applying the animal glue to the .paper at a relatively high pH value of between 8 and 9.5. This is accomplished by soaking and dispersing the glue in the proper concentration of an alkali such as sodium hydroxide. The amount of alkali will vary with the glue that is used, and the properties of the glue in turn depend upon the processing of the glue during its preparation and manufacture.

' Uniformity of properties of the sizing depends upon the proper buffering of the glue size at the required uH values, and the lowered temperature of the size as applied, which latter factor is more subject to control in the type of equipment used (or tub sizing than is possible when elevated temperatures are utilized.

An increased wet strength of the paper is obtained by employing glue of high pH, such as has been described above, which is more rapidly and completely tanned by such materials as formaldehyde than is glue of a pH value of 4.5 (substantially the iso -electric point) It has also heretofore been sought at times to apply a wetting agent to the paper to eliminate the last traces of white spots in the blueprints. It has been presently discovered that not all wetting agents are of value for this purpose but only those commonly known as cationic wetting agents accomplish the desired effect. Those found to be of particular value with blueprint coating solutions are tertiary amines or the quaternary salts of tertiary amines.

The high pH glue size can be prepared in several ways, with sodium, potassium or ammonium hydroxides, and it has also been prepared with other materials that are alkaline in nature. Successful glue sizings have been prepared. for example, with tertiary amines in place of the abov mentioned hydroxides.

As an example of the method in which the glue size is prepared, the following illustration may be given. Sodium hydroxide, 646 grams, was dissolved in 440 gallons of water to which was added 316 pounds of animal glue of good 'quality and the glue allowed to swell in this solution for several hours. The glue was then heated to 140 degrees F. to 160 degrees F. to completely disperse the glue. This dispersion of glue was added hot and with rapid stirring to a dispersion of 4.25 pounds of borax and 8 pounds of a high grade of bentonite in '75 gallons of water per 100 gallons of glue size. It has been found of great importance to add the glue dispersion precipitation. By the time these two dispersions are mixed, the system has cooled to about the proper temperature for sizing which, according to this invention is between 90 degrees and 115 degrees F. This mixture can be kept for several hours in its concentrated condition, preliminary to its employment. Before employment, it is diluted with water of the proper temperature, so that the material is brought to a concentration of substantially 2.8 to 4.5 degrees Beaum and to the temperature for employment, which preferably is between 90 and 110 degrees F. and should be below 125 degrees F. In this condition, it is placed in the size tub of the coating machine; and the paper is passed through it at a rate of substantially 2'75 to 375 feet per minute; and then moved over the usual press rolls of the machine for stripping off excess coating material, and then may be passed through an aqueous solution containing about 2 perccnt of either glyoxai or form to the bentonite dispersion to avoid aldehyde and between 0.02 and 0.5 percent of the tertiary amine wetting agent. This solution has been found advantageous in practice, as it permits a very rapid tanning of the glue sizing, and facilitates the machine work of coating, tanning and drying, without demanding long times of tanning treatment. The excess is again squeezed oil and the paper is then dried.

The quantity of bentonite employed may be varied from 12 pounds downwardly. It is preferred to employ a relatively large quantity of bentonite, to assure a maximum of its action during the coating operation: but a limitation upon the quantity is established by the inability of the sizing solution to maintain the bentonite in uniform suspension, and hence a quantity of 2 to 10 pounds, in the above formula, is presently regarded as an optimum, in giving a maximum effect in the coating with a minimum liability of settling in the course of the sizing operation. However, it has been found that a quantity of less'than one pound has substantially no effect.

It has been found in practice that one of the Ninols is satisfactory as a wetting agent, these substances being commercially available tertiary amines derived from monoand diethanolamines. It has also been found that tertiary amine derivatives of ,oleic, stearic and like fatty acids may be employed: and in general it ha been found that tertiary amines, as such. or in the form of their quaternary salts with diethyl sulfate, may be employed. It is not essential to use the wetting agent in all cases, and if so desired, the paper may be aged for a certain time interval between the sizing operation and the application of the tanning agent.

The borax as a buffer is indicated as employed in the quantity of 4.25 pounds for the above formula, which may be regarded as an excess over that required for treating wood pulp papers which are low in alum: but has been found adequatefor the sizing of 100 percent rag papers which are high in alum. Such excess of borax has not been found to disturb the proper action of the sizing solution upon the wood pulp stock,

and hence it is preferred to employ the borax in excess. to assure that solutions of the type of these formulas can be employed upon either wood pulp or rag stock papers without substantial change therein.

As indicated in the above examples, the stock sizing is made up in a relatively concentrated form, and can then be kept for normal periods of time. It has been found preferable to maintain it at a temperature of degrees or above, toavoid gelation difficulties. It is desirable to include 0.5 percent of the weight of the glue of a preservative such as sodium ortho-phenylphenate. Preferablyv immediately prior to employment, it is diluted with water to the strength desired for the particular sizing operation, having due regard to the condition of the paper stock and to the selected speed of movement of the stock through the sizing operations. Thus, if the stock is found to be more open or porous (for example, by a lower degree of engine sizing) than the paper which was previously sized, it is preferable to employ less diluting water and to use the sizing solution at a higher Beaum. It has been found, however, that the sizing solutions described in the present examples can be employed with many diiferent grades of paper of the so-called blueprint, negative, and bond types, without change of the proportions therein, and within the aforesaid ranges of glue strength. In

2,320,771 general, for example, it is found that a sizing tity of alkali will vary with the particularalkali and the quality of the animal glue used. The preferred buflerused is borax, although magnesium oxide, magnesium carbonate or other materials or combinations may be employed to maintain the pH of the glue size within the limits of about 8 and 9.5, and the quantities of buii'er used will depend upon the amount of paper to be sized with a given quantity of the size: it

has .been found, however, that the magnesium-- bases cause a progressive undesirable thickening it the sizing solution is not a few hours.

consumed within It is obvious that the invention is not limited to the illustrative examples shown, but that it may be practiced in many ways within the scope of the appended claims.

I claim:

1. A paper sizing consisting of an aqueou solution having a density and a pH of 8.0 to 9.5 and containing 3 to 8% percent of animal glue, an alkali and an alkaline buflering agent for maintaining the solution at said pH; and having between substantially A and 1% percent of bentonite suspended therein.

2. A paper sizing consisting of an aqueous solution having a density of 2.8 to 4.5 degrees Beaum and a pH of 8.0 to 9.5 and containing 3% to 8% percent of animal glue, an alkali and substanof 2.8 to 4.5 degrees Beaum face sizing coating upon tially percent of borax as a. buiicring agent for maintaining the solution at said pH, and having between substantially and 1% percent of bentonite suspended therein.

3. The process of preparing a paper sizing which comprises preparing a hot alkaline solution of animal glue and a suspension of bentonite in aqueous borax solution, gradually adding the glue solution to the bentonite suspension while stirring, and maintaining perature in excess of 80 during use. 4. A paper tub sizing for providing a dry surface sizing coating upon blueprint, negative, and bond papers, comprising an alkaline aqueous solution .containing 3% to 8 percent of animal glue and an alkaline buffering agent for maintaining the pH thereof at 8.0 to 9.5 by resisting the-'eli'ect of aluminum sulfate dissolved from the paper during the coating operation, the solution having a. density of 2.8 to 4.5 Beaum at a temperature between 90 and 1 15 degrees F.

5. A paper tub sizing for providing a dry surblueprint, negative, and bond papers, comprising solution containing 3 glue and substantially the mixture at a temdegrees F. prior to and to 8 percent of animal /2 percent of borax, the

solution having a density of 2.8 to 4.5 Beaum' at a temperature between 90 to 115 degrees F.

6. A paper tub sizing consisting o1 an aqueous solution having at a temperature of 90 to 115 degrees F. a density of 2.8 to 4.5 degrees Beaum and a pH of 8.0 to 9.5 and containing animal glue, alkali and a soluble alkaline bufl'ering agent. and having substantially A, to 1% percent of bentonite suspended-therein.

PAUL B. DAVIDSON.

an alkaline aqueous 

